Sectionalized waveguide system



March 1, 1960 J, RAY 2,927,288

SECTIONALIZED WAVEGUIDE SY STEM Fil ed Jan. 8, 195a vi 4\ m7/////////////////////////4\ 4 2,927,288 Patented Mar. 1, 1960 SECTIONALIZED WAVEGUIDE SYSTEM John Ray, Indianapolis, Ind. Application January 8, 1958, Serial No. 7 07,837

10 Claims. (Cl. 33398) (Granted under Title '35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This application is a continuation-in-part application of the application of John Ray, Serial No. 258,973, filed November 29, 1951, for Pressurized Waveguide System.

This invention relates to tubular electromagnetic wave conductors or waveguides of microwave energy and more particularly to waveguide sections and couplings for producing systems in which each section is individually fluidly sealed for coupling in sequence in a system wherein the fluid seals of adjacent sections are impedance matched for the transmitted microwave energy. As a result of such matching the discontinuities are decreased and the efiiciency is increased twentyive percent or more in the transfer of microwave energy from source to load.

The use of a pressurized waveguide system is broadly old in the art, the pressurized system being usedfor protection of the system from moisture, fungus growth, and corrosion during inactive periods and during the operation of the equipment. The prior art systems comprise a singular pressurized system. If, for any reason, a part of the waveguide system develops a leak or is otherwise damaged, the leaky or damaged section must be removed, thereby completely exposing the rest of the waveguide system to the atmosphere. This results in the contamina tion of the whole system and causes added expense and time in repairs. In such a system, for example, an air pump must accompany the apparatus, including the pres surized waveguide system, which increases the weight and cost of a given installation. It is also known in the art to pressurize a particular section of a waveguide individually for the accommodation of certain microwave control elements, as attenuators, phase shifters, cavity resonators, or the like. While individual sections of a system may be individually pressurized for these control elements, the problem arises as to the means of electrically matching the fluid closure means on each end of the waveguide section.

In the present invention waveguide sections have been produced which are fluid-tight to be pressurized, evacuated, or gas filled, as desired, each section having coupling components on each end thereof that are attachable to companion coupling components on other sections to produce a waveguide system. Each waveguide section has an electromagnetic transparent window fluidly sealing each end of the waveguide section, one window consisting of a resonant window material, such as glass, in a frame of material with the same coefiicient of expansion, and the window in the other end of the wavequide section consisting of a non-resonant material, such as mica, Teflon, Kel-F, polystyrene, or a similar non-resonant material. The coupling component on the end of the waveguide section having the resonant material is companion only to the coupling component on the waveguide section having the non-resonant material so that the waveguide sections may only be coupled as a composite coupling in a system with the dissimilar electromagnetic transparent windows in juxtaposed position for matching the impedances of the waveguide sections. The design details for resonant electromagnetic windows are more fully discussed in volume 9 of the Massachusetts Institute of Technology, Radiation Laboratory Series, entitled Microwave Transmission Circuits, published by McGraw-Hill, 1948 edition, on pages 220 to 222. The companion couplings are also of a tolerance, when assembled, to exactly position the dissimilar electromagnetic transparent windows in close air-spaced relation such that the sum of the thicknesses of both of these windows and the air-space is approximately one-half wavelength of the microwave energy transmitted through the waveguide system. While this sum of the windows and the air-space may be used in multiples of one-half wavelength, the use in multiple half wavelengths would reduce the efficiency of the system. The present invention of coupling used separately, as shown and described, is superior to the prior art of wave guide coupling technique inasmuch as the efficiency of microwave power transfer is greatly increased. By such waveguide sections any system may be readily repaired where there is damage of a section or sections without contamination of the system with moist or other contaminated air and without the necessity of re-pressurizing or re-evacuating the system after a repair is made. Further, these sections of waveguide may be stored or transported without any special covering or enclosures since each section is independently sealed. One coupling component of each companion coupling has a choke means therein of approximately one-quarter wavelength to compensate for any mechanical or machining inaccuracies of the parts. Further, each waveguide section is readily adaptable to receive a magnetron or other power source on either coupling component, which makes a system of such waveguide sections readily adaptable for the introduction of power, as in an antenna system or the like. The sections can be constructed for round or rectangular waveguides alike, and may also be produced in sizes to transmit electromagnetic energy in the L band, S band, X band, K band, K band, K band, or any other band as desired. The sections are also readily adaptable for accommodating changes of microwave frequency or mode of operation since the glass window or resonant electromagnetic window is removable so that difierent sizes of windows to produce different capacitive-inductive reactance may be placed in one end of the waveguide. By this arrangement a waveguide system may be produced from these sections wherein there is very little attenuation or reflection of the microwave energy approaching that of the efficiency of unobstructed waveguide systems. It is therefore a general object of this invention to provide a waveguide system of individually fluidly sealed waveguide sections, and the art of coupling, coupled in a composite manner to provide an unattenuated microwave path resulting in a highly efficient system or coupling.

These and other objects, advantages, features, and uses may become more apparent as the description proceeds when considered along with the accompanying drawing in which:

Figure 1 shows a side elevational view of a sectionalized waveguide system incorporating the invention;

Figure 2 is a longitudinal cross-sectional enlarged view of one of the companion coupling means separated to reveal the parts arrangement;

Figure 3 is a cutaway sectional view greatly enlarged of a portion of the companion coupling components shown in the coupled position;

Figure 4 shows an enlarged cross-sectional, partially elevational view taken on the line 4-4 of Figure 1 looking in the direction of the arrows;

Figure 5 shows an enlarged partially elevational and partially sectional view of the waveguide taken on the line 5-5 of Figure 1 looking in the direction of the arrows;

Figure 6 shows an elevational view of the framed resonant electromagnetic window shown in section in Figure 2; and

Figure 7 shows the gasket for the electromagnetic window of Figure 6, as arranged in cross section in Figure 2.

Referring more particularly to Figure 1, there is shown a plurality of waveguide sections 10 in assembled relation, each waveguide section consisting primarily of a waveguide tubular conductor or conduit 11 having a coupling component 12 on one end and a coupling component of two parts or flange members 13 and 14 on the other end. Since each waveguide section 10 is identical, the same reference characters will apply for each of the sections. As will hereinafter be made clear, each waveguide section is individually fluidly sealed and may be pressurized or evacuated through a tube 15 communicating with the interior of each waveguide tubular conductor. The companion coupling component 12 is coupled with the companion coupling component 13, 14 by bolts 16 extending through the corners or outer peripheral portions of the coupling components with the outer end of each bolt having a nut 17 threaded thereon to provide a composite coupling. It is to be understood that cap screws or other well known mechanical means could be used in lieu of the means 16, 17 without departing from the spirit of this invention.

Referring more particularly to Figures 2 and 3, arrangement of parts in the waveguide section may be more readily understood by these cross-sectional views. In Figure 2 the companion coupling components are disconnected and slightly separated for the purpose of clearly illustrating the arrangement of parts. The coupling component part 13 consists of a flange that is secured to one end of the waveguide electromagnetic conductor 11, as by welding, brazing, or the like, 2%. The flange member 13 is placed inwardly from the end of the electromagnetic wave conductor 11 a suflicient distance to receive the part or flange member 14 over the end of this conductor 11. The flange member 14 has a passage 21 exactly fitting over the exterior surface of the conductor 11, the passage 21 having a reduced passage 22 equal to the inner dimensions of the conductor it; to produce a shoulder 23. The flange element is of the coupling component is removably supported against the flange member 13, as by cap screws 24 passing through holes in flange member 13 and threaded into tapped bores in the flange member 14. Between the end of the conductor 11 and the shoulder 23 is supported an electromagnetic transparent window 25, such as glass or mica, sealed in a frame 26 of Kovar, Fernico, or other material possessing the expansion coeflicient of the window 25, producing a resonant window. The electromagnetic transparent window and its frame are positioned against a gasket 27 placed over the end of the conductor 11 to cushion and seal the electromagnetic transparent window in the waveguide section. In the face 29 of the coupling component member 14 adjacent the coupling component 12 is an annular groove 28 for receiving a portion of the coupling component 12, soon to be described.

The coupling component 12 on the adjacent waveguide conductor 11 is likewise flxedly attached to the conductor 11, as by welding, brazing, or the like, 30 with the inner face 31 thereof being in alignment with the inner end of the waveguide conductor 11. Extending inwardly from the face 31 of the coupling component 12 and parallel to the waveguide conductor 11 is an annular cavity, or groove, 32 providing a high frequency choke which effectively places a low impedance between the waveguide sections and compensates for machined discontinuities when the waveguide sections 10 are coupled, as will be made clear hereinafter. While the cavity 32 is illustrated as being annular, it should be understood by those skilled in the art that semi-annular or other configurations may be used to accomplish the choke properties. in the outer periphery of the coupling component 1'2 is an internal annular threaded portion 33 providing a shoulder 34, the plane of the shoulder being slightly removed outwardly from the face 31, the reasons for which will be made clear hereinafter. Against the shoulder 34 is placed a non-resonant electromagnetic transparent window 35 which may be of mica, Teflon, Kel-F, polystyrene, or other suitable non-resonant material, mica having been found preferable in this application of conducting microwave energy. The non-resonant window 35 is held in place by a threaded ring 36 holding the periphery of the non-resonant window material 35 securely against the shoulder 34, the shoulder 34 being in a plane slightly removed from the face 31 providing a radial space for communication between the interior of the waveguide conductor 11 and the annular groove 32 whereby choking operation may be accomplished for the assembly. The peripheral portion 37 supporting the nonresonant electromagnetic window with the ring 36 screw threaded therein is made to fit exactly within the annular groove 28 in the coupling component member 14 so that when the companion component parts of the coupling are supported together, as by the bolts 16, 17, or other suitable means, the outer face of the non-resonant electromagnetic window 35 will rest against the outer face 29 of the coupling component member 14, as more particularly shown in Figure 3 in the assembled condition. As more particularly illustrated in Figure 3, the coupling components are so arranged that in the assembled condition the distance from the opposite face of the electromagnetic transparent window 25, as shown by the arrow 4%, to the opposite face of the non-resonant window 35, as shown by the arrow 41, including the air-space therebetween, is made to measure about one-half wavelength of the microwave energy transmitted through the system. This arrangement is one important feature of this invention in that this structure avoids reflections of the microwave energy which would cause a voltage standing wave ratio (VSWR) between the junction members and in that it also prevents arcing and shorting of the sections at the higher power levels.

Again referring particularly to Figure 3, a partial or broken away view of Figure 2 is shown wherein the two coupling components are joined in fixed composite relation by the bolts and nuts 16, 17 or other suitable means to draw the peripheral portion 37 with the annular ring 36 thereon within the annular channel 25 of the flange member 1 2' so that the non-resonant window 35 rests against the face 29 of the flange member 14. This produces a space between the electromagnetic transparent windows equivalent to the longitudinal distance of the opening 22 in the flange member 14. Also, the threading home of the cap screws 24 draws the frame 26 with the electromagnetic window 25 therein tightly against the gasket 27 to support this window in the coupling component 23, 14 in a stationary manner. The annular ring 36 supports the non-resonant electromagnetic transparent window 35 in a fixed relation with the coupling component 12 such that these coupling components may be drawn together, as shown in Figure 3, or separated, as shown in Figure 2, without any loss of vacuum or fluid within the waveguide sections 11. it is to be understood that the coupling component 13, 14- with its electromagnetic transparent window 25 is on one end of each waveguide section it), and the coupling component 12 with its electromagnetic transparent window 35 is on the other end of each waveguide section 10. The coupling of the coupling components, as shown in Figure 3, brings the electromagnctic windows 25 and 35 in close air-spaced relation, providing the distance shown by the arrows 40 and 41, which is designed to be approximately one-half wavelength of the microwave energy transmitted, as hereinbefore stated. The electromagnetic transparent windows aaa'aass are air-spaced to prevent any arcing or shorting at higher power levels although ambient pressures and temperatures may vary.

Figure 4 is a cross-sectional view of the waveguide conductor 11, as shown in Figure 1, taken on the line 4-4 looking in the direction of the arrows. By this view the coupling component 13, 14 is shown in elevation with the cap screws 24 arrangement shown for holding the coupling component parts 13, 14 in an assembled condition. Within the waveguide conductor 11 may be seen the resonant electromagnetic window 25 in its frame 26.

Figure 5 shows a cross-sectional view of the microwave conductor 11 taken on the line 55 of Figure 1 looking in the direction of the arrows. In this view the coupling component 12 is shown in elevation with the nuts and bolts 16 and 17 in each of the four corners supporting this coupling component on the coupling component 13, 14. The portion of the coupling component 12 concentrically within the nuts and bolts 16 and 17 and around the microwave conductor 11 is shown to be a circular enlargement to provide means for the annular cavity 32 within the coupling component 12 although other configurations, as square or rectangular, may be utilized if desired. The cavity 32 could be of other configurations, as square or semi-annular, or otherwise, as is well known in the art. Looking into the microwave conductor 11, as seen in this figure, a central portion of the non-resonant window 35 will be seen in elevation. Although Figures 4 and 5 show a rectangular waveguide conductor 11, it is also to be understood that this invention is equally applicable to circular or other cross-sectional configurations of waveguide conductors.

Referring to Figure 6, there is shown the resonant electromagnetic window 25, which is of glass, silica material, or other suitable dielectric material, 25 having the proper resonant qualities, mounted within a framework of Kovar or Fernico 26 or other material having the same coefficient of expansion as the material 25. Window sizes and thicknesses of the dielectric material for the capacitanceinductance produced is calculated for the resonance of the frequency required. In addition to the electrical properties, the dielectric thickness should be suflicient to withstand pressures expected in the waveguide sections to which it will be exposed. The design details for such a window are more fully disclosed in aforementioned volume 9 of the Massachusetts Institute of Technology, Radiation Laboratory Series book.

Figure 7 shows a gasket of rubber or other suitable resilient material for mounting the window of Figure 6 within the coupling component 13, 14. By having the resonant electromagnetic transparent window 25, 26 removable from the coupling component 13, 14, windows of different glass or silica areas can be readily inserted in the waveguide sections to provide resonance for microwave energy for different modes and frequencies since the window 25, 26, designed for a certain frequency range and mode, will have less attenuation and reflection characteristics of the microwave energy transmitted.

In the operation of the waveguide system a plurality of waveguide sections 10 is coupled by the bolts and nuts 16, 17, or other suitable means, to produce the system desired. Each waveguide section is constructed, as shown and described hereinbefore, whereby each section is closed by a fluid-tight seal on opposite ends of each waveguide section 10, the right end being closed by the coupling component 13, 14 with the resonant electromag netic transparent window 25, 26 therein and with the left end of each waveguide section 10 being closed by the non-resonant window 35. Each waveguide section 10 may be individually evacuated, pressurized, or gas filled, as desired, through the tube 15. With the system coupled with waveguide sections 10, as shown, microwave energy may be conducted therethrough with little attenuation or dissipation of the energy passing through thecoupled joints. By using resonant and non-resonant electromagnetic windows, separated by a small air-space sufiicient to avoid arcing or shorting between the sections and of a distance apart from the outer surfaces equivalent to about one-half wavelength of the microwave energy transmitted, the impedance of the system is efficiently matched over a fairly wide range of microwave frequencies. The choke groove 32 is in communication with the waveguide conductor 11 through the passage between'the face 31 of the coupling component 12 and the non-resonant window 35 and is a high frequency choke for placing a low impedance between the waveguide sections 10 to compensate for any mechanical or machining inaccuracies of the coupling parts. This choke cavity is designed to be approximately one-quarter wavelength of the microwave energy transmitted.

If at any time any one or more sections 10 of the waveguide system are damaged, as by enemy gun fire or the like, new sections may be placed in this system without the necessity of re-pressurizing or re-evacuating the system by auxiliary pumps and without the necessity of drying the fluid within the system since each section 10 is fluidly sealed individually. By being able to replace damaged sections of a waveguide system, the waveguide system may be put into immediate operation under combat conditions which would not always be possible under conditions where auxiliary pumping and air drying means are needed. It is of extreme importance in combat to return the radar or other systems to service in shore installations, in ships, or in aircraft, or wherever such waveguide systems are required for combat use, in the shortest time possible. It is also to be understood that a Waveguide system may consist of a single waveguide section where the couplings are completed to make the matched composite coupling of this invention.

It is also important in this invention that microwave energy sources, such as magnetrons, may be readily adapted for coupling to either coupling component 13, 14 or coupling component 12, and no attenuation, power leakage, or other detrimental effects will result in so coupling an energy source. Although the Waveguide sections 10 are shown as being straight, it is also to be understood that this invention is equally applicable for curved sections, twisted sections, or compounded twisted and curved sections. This waveguide system was designed to operate efficiently over a temperature range from 65 C. to C. although modifications may be made to raise or lower this temperature range as by the change of materials, the use of materials to provide expansion and contraction compensation, and the like.

While many modifications and changes may be made in the constructional details and features of this invention, the invention being merely illustrated in one preferred form, I desire to be limited in my invention only by the scope of the appended claims.

I claim:

1. A waveguide system of individually fluidly sealed Waveguide section means comprising: waveguide section means having companion coupling means for coupling said sections to form a system, each waveguide section means fluidly closed by a resonant electromagnetic transparent window on one end and a non-resonant electromagnetic transparent window on the other end, and said companion coupling means being arranged to couple only said one end of one section means with said other end of another section means to position said resonant and non-resonant electromagnetic windows in air-spaced relation equivalent to about one-half wavelength through the window surfaces and the air-space for matching the impedance of the waveguide sections whereby the waveguide characteristics for the system remain unchanged for changing atmospheres.

2. A waveguide system of individually fluidly sealed waveguide sections comprising: a plurality of waveguide sections; coupling parts on opposite ends of each waveguide section, each coupling part on one end of each section being companion to each coupling part on the other end of each waveguide section for coupling said sections in series, said one and other ends respectively of adjoining waveguide sections being juxtapositioned; and electromagnetic transparent windows fluidly closing opposite ends of each waveguide section, one being resonant and the other being non-resonant for each waveguide section and correspondingly related to said one and other ends of each waveguide section, said companion coupling parts, when joined, positioning adjacent resonant and non-resonant windows in air-spaced relation equivalent to one-half wavelength of the electromagnetic energy transmitted for matching the impedance of the waveguide sections thereby avoiding microwave energy reflections tending to cause a voltage standing wave ratio between waveguide sections whereby the waveguide characteristics for the system remain unchanged for different atmospheres and higher power levels.

3. A waveguide system as set forth in claim 2 wherein said electromagnetic transparent windows are removably fixed in the coupling parts, the resonant window being removable for replacement of windows of different dimensions to accommodate different frequency ranges and modes of operation of conducted microwave energy.

4. A waveguide system as set forth in claim 3 wherein said resonant electromagnetic window is glass and said non-resonant electromagnetic window is mica.

5. A waveguide system of individually fluidly sealed waveguide sections comprising: a waveguide consisting of at least one waveguide section; coupling components on each end of each waveguide section, each coupling component on one end of each waveguide section being dissimilar and companion to each coupling component on the other end of each waveguide section for coupling at least one waveguide section in a system having said companion couplings; an electromagnetic transparent window removably supported in each. coupling component, one window being resonant in one of the companion coupling components and the other window being non-resonant in the other of the companion coupling components to provide closely air-spaced resonant and nonresonant windows at each companion coupling of said waveguide section, said waveguide section being fluid tight for receiving fluid at desired pressures; and a choke cavity in at least one of said coupling components for providing a high frequency choke to place a low impedance between the waveguide sections for the compensation of inaccuracies in construction of the companion couplings thereby minimizing attenuation of transmitted energy whereby a waveguide including a waveguide section may be removed and replaced in a waveguide system without affecting the sealed condition of the remainder of the system and without disturbing the electrical characteristics of the coupled waveguide section in the system.

6. A waveguide system as set forth in claim 5 wherein said resonant window is of dielectric material and said non-resonant window is of electrical insulating material, and each companion coupling supports said resonant and non-resonant windows such that the sum of the window thicknesses and the intermediate air-space is approximately equal to one-half wavelength of the microwave energy conducted through the windows and the intermediate air-space.

7. A waveguide system as set forth in claim 6 wherein said resonant window of siliceous material is fixed in a frame of equivalent coeflicient of expansion with the window area of predetermined size.

8. A waveguide section for coupling with other like waveguide sections to provide a waveguide system comprising: a length of tubular waveguide conductor; a coupling component on each end of said waveguide conduotor, said coupling components being dissimilar and companion; a resonant electromagnetic transparent window supported in one of said companion coupling components and a non-resonant electromagnetic transparent window in the other of said companion coupling components, each window being normal to the longitudinal centerline of said waveguide conductor whereby the waveguide section is fluid tight for retaining fluid therein under predetermined conditions of pressure and moisture; means on each coupling component for removably attaching each resonant and non-resonant window in said coupling component; and an annular electromagnetic choke cavity in one of said coupling components and in electromagnetic energy communication with said waveguide conductor providing a high frequency choke adapted to place a low impedance between coupled waveguide sections whereby fluidly sealed electrically matched waveguide conductor sections are produced for coupling in series.

9. A waveguide composite coupling for coupling sections of fluidly sealed waveguide conductors comprising: separable companion coupling components having a microwave passage therethrough, each for being fixedly attached to a section of waveguide conductor in said microwave passage; a resonant electromagnetic transparent window removably fixed across the microwave passage of one coupling component and a non-resonant electromagnetic transparent window removably fixed across the microwave passage of the other coupling component, said windows being longitudinally positioned in said microwave passages to bring them into close airspaced relation such that the sum of the window thicknesses and the air-space is about one-half wavelength when said coupling components are compositely assembled for matching the impedance of coupled waveguide sections to avoid microwave energy reflections tending to cause a voltage standing wave ratio between waveguide sections; and an annular choke groove in one of said coupling components about, and in communication with, said microwave passage for producing a high frequency, low impedance choke between waveguide sections coupled by said composite coupling thereby minimizing attenuation of transmitted energy whereby the ends of waveguide sections are fluidly sealed and the impedance is matched for the waveguide sections.

10. A waveguide composite coupling as set forth in claim 9 wherein said resonant window is glass fixed within a frame of material of equivalent coeflicient of expansion, said resonant window and its frame being removable by a separation of two parts constituting said one coupling component; and wherein said non-resonant window is mica extending over the area of said microwave passage and said annular choke groove.

published in Electronics, May 1954, pages -171. 

